migrated_tools_conf should be in mutable_config_dir

[jdavcs]

This used to be in config_dir by default, but should be in mutable_confiig_dir.

1. Keep it consistent with ansible-galaxy. (as per discussion with @natefoo)
2. Also, correct description of integrated_tool_panel_config (unrelated minor fix)

Context:

• current ansible-galaxy: https://github.com/galaxyproject/ansible-galaxy/blob/master/defaults/main.yml#L192
• galaxy's config/__init__.py as it used to be prior to [19.09] Fix autocreation of shed_*_conf.xml #8610: be5aafd#diff-46f86ea0d82b84642e4218279ef61442L209

[jdavcs]

Failed unit test is unrelated. All pass.

[nsoranzo]

• Given [19.09] Fix autocreation of shed_*_conf.xml #8610 targeted 19.09, shouldn't this also target that release?
• You need to also execute make config-rebuild and commit the changes.

[jdavcs]

@nsoranzo do you mean target only that release, or target dev + 19.09 (and then 20.01 too?)

[mvdbeek]

Just 19.09 is fine, we can merge forward then.